1. Field of the Invention
This invention pertains to arc welding, and more particularly to adjustable nozzle arc welding guns.
2. Description of the Prior Art
A vital component of every wire welding system is the welding gun. In addition to supplying welding wire and electrical power to a workpiece, the gun also directs a stream of inert gas that shields the welding arc. Consequently, wire welding guns are required to accommodate an interplay of mechanical, electrical, and fluid systems.
The welding wire is fed through the welding gun body and through an elongated welding contact tip. The welding contact tip terminates approximately at the location of an orifice of a nozzle that directs the shielding gas to the region of the weld. The dimensional relationship between the end of the contact tip and the nozzle orifice is an important parameter of the welding process. It is desirable that the welding gun be designed to provide an adjustable dimension between the nozzle orifice and the tip so that the gun can be used with many different welding applications. It is also highly desirable that the dimensional relationship, once it is made, remain fixed for the duration of a welding job. At the same time, the adjustment must be convenient to change when needed to suit a different welding requirement.
In practice, the forgoing goals are difficult to achieve. A major factor that must be considered when designing a wire welding gun is that welders are prone to striking the gun against a hard surface to remove weld spatter buildup at the contact tip and the nozzle. To solve the adjustment problem, many prior wire welding guns are designed with nozzles that are fixed relative to the gun body and that use different length welding contact tips that are interchangeable with each other. The contact tips are invariably fastened by some mechanical means into the gun body. A tip of the desired length for the job at hand is secured into the body, and it is replaced with a different length tip when required for a different job. The fixed-nozzle multi-tip solution has disadvantages. One disadvantage is that an inventory of different length tips must be kept on hand, which is undesirably expensive. Another disadvantage is that for many jobs the available tip lengths may only approximate the desired length. Unless a supply of tips having very small length increments is stocked, the welder must often be satisfied with a tip of other than optimum length.
Another prior solution to the tip-orifice dimensional problem was to employ a single length tip but an adjustable nozzle. Nozzle adjustment was usually achieved by means of mating threads on the nozzle and another part of the gun body. By rotating the nozzle, its axial position relative to the contact tip was changed. Although the adjustable nozzle-fixed tip design could provide a correct dimensional relationship between the tip and the nozzle orifice, it was very difficult to maintain. The threads were easily damaged, and the parts were prone to seizing together from dirt and other foreign matter. In addition, the threaded nozzle design was undesirably expensive.
Another unsatisfactory prior attempt to provide adjustability between the nozzle and welding contact tip was a slide-on nozzle that fit by friction over a portion of the gun body. The slide-on nozzle was slidable relative to the contact tip to provide very fine adjustments. However, the slide-on nozzle had no positive stops to maintain an initial desired location of the nozzle relative to the contact tip. As a result, the nozzle was prone to slide out of position during the course of normal welding operations.
Thus, a need exists for a wire welding gun with improved capabilities for tip-nozzle adjustment.